 |
|
 |
|
 |
|
 |
|
 |
|
 |
|
 |
|
 |
|
 |
|
 |
|
 |
|
 |
|
 |
|
 |
|
 |
|
|
US EPA SITE Program Data
A Table in the draft “SITE Technology Capsule” summarizes the data:
Conventional
Asphalt
(cm/sec)
(3 mm wide, 2.5 cm long cracks)
(MegaPascals)
(60 days) (cm/sec)
(Depth of Penetration, cm)
(drainage layer only)
(cm/sec)
Notes:
1 Method developed by Ronald Terel of WCC 2 Cracking was initiated at 7.2mm of deflection AASHTO American Association of State Highway and Transportation Officials ASTM American Society for Testing and Materials Two types of data were gathered to establish that MatCon surpassed the RCRA Subtitle C water infiltration standard of 1 x 10-7 cm/sec: field data was generated by monitoring volumes of water in a collection sump fed by the central drainage layer of a three-layer MatCon cell during rainfall events and, second, with laboratory testing according to ASTM D-5084, the same test protocol used to evaluate clay liner materials. The SITE Technology Capsule reports that Field data obtained to date at the Dover and TCL sites indicate that the field permeabilities are 1.22 x 10-8 cm/sec and 4.24 x 10-8 cm/sec, respectively, exceeding the RCRA C standard. Similarly, all the laboratory evaluation of core samples taken from the two sites showed permeability exceeding this RCRA standard.
The SITE data is especially striking in its comparison of MatCon to conventional asphalt, the EPA concluded that MatCon is significantly better than conventional asphalt covers in relation to permeability, flexure, load/deformation thermal crack resistance, tensile strength and aging/degradation properties. The EPA’s SITE Technology Capsule summarizes the data in this way:
“A pilot-scale MatCon cover was installed at the Dover site in April, 1999 together with an adjacent conventional asphalt cover for comparative testing. Laboratory testing results indicate that the permeability of the MatCon cover at Dover is less than 1 x 10-8 cm/sec, whereas the permeability of the adjacent conventional asphalt cover is between 5.0 x 10-5 cm/sec and 1 x 10-4 cm/sec. Flexural tests of samples of the MatCon and the conventional asphalt covers indicate that the MatCon cover can tolerate three times more deflection without cracking compared to conventional asphalt.”
MatCon achieves its low permeability by reducing air voids to a level where they do not interconnect. Two photographs of cross-sections of MatCon and conventional pavement, with air voids indicated by fluorescent epoxy, tell the story.
A special bending beam test was developed to demonstrate to measure flexural strength, and thereby evaluate MatCon’s ability to conform to underlying conditions such as differential settlement. The data shows that the conventional asphalt specimen began to crack after only eight days and seven mm of deflection. The MatCon beam showed no signs of cracking with 21 mm of deflection after 30 days—the point in time at which the conventional asphalt beam failed. In an independent test extended to 90 days, the MatCon beam deflected a full 30 mm without cracking, this would be tantamount to 1.64 foot deep depression over a 25 foot span, or a 6.56% slope.
When conventional asphalt was first considered as an environmental containment material more than a decade ago it was rejected, in part, because it is to sensitive to temperature changes and thermal cracking. As you can see in a Temperature/Viscosity curves. conventional asphalt (yellow line) is a liquid at 300º when it is mixed, but at very low temperatures can be as brittle as glass. Ideally asphalt would look like the white line, with the same viscosity or stiffness at all temperatures below that required for mixing. While that is not possible, the dotted red line shows how the suite of modifiers in MatCon both increase stiffness in hot weather and elasticity in arctic climates. MatCon’s superior resistance to low temperature thermal cracking was established using ASTM and AASHTO test protocols. The resistance to thermal cracking was determined by fixing sawed beam specimens of MatCon and conventional asphalt between rigid end platens and gradually lowering the temperature in the chamber. During this test, the stress builds because the specimen is shrinking and eventually breaks. The results show that MatCon is 38% stronger that conventional asphalt at failure and resists cracking until reaching a temperature 8 degrees F lower; this would represent an improvement of two full grades for low temperature performance under the PG grading system.
Another piece of SITE data provides a explanation for MatCon’s superior performance in differential settlement and resistance to thermal cracking: MatCon’s TENSILE STRENGTH was found to be 1.74 times better than conventional hot mix using the ASTM D-4123.
Thermal cracking is a cold weather phenomenon. Even in temperate climates, aging occurs due to oxidation caused by exposure to air and water. Asphalt molecules increase in size, resulting in hardening and decreased resistance to cracking, raveling and erosion. The SITE program data comparing aging properties of MatCon to conventional asphalt were generated by exposing 4” core samples taken from the Dover AFB installation to ultra-violet light and periodic water sprays over a 60 day period, simulating weather cycles and rain events. As you can see in this chart both MatCon and conventional asphalt exhibit initial stiffening due to structuring or steric hardening. After that, the conventional material begins to deteriorate due to water and air entering the void structure. The MatCon data becomes essentially flat, indicating a stable, unchanging condition.
For more information, please contact us at MatConinfo@wilderconstruction.com
1525 E. Marine View Drive | Everett, WA 98201-1927
(425) 551-3100 fax (425) 551-3116
© 2003 Wilder Construction Company webmaster@wilderconstruction.com
Last updated March 20, 2002
web site design and management by WEB518/Marc Rapaport